A fringe locking phenomenon in a two beam interferometer using a semiconductor laser subject to optical feedback has been observed, whose injection current is modulated. When a path difference of the interferometer is sufficient, fringes taken by a CCD camera are seen to be stationary and the rms fluctuations of fringe phase is reduced to as low as 0.2 (pi) radians from more than 9 (pi) radians that is observed without the optical feedback. The rms phase fluctuation is independent of frequency and amplitude of the current modulation. The fringe locking has also been observed in the presence of both injection current modulation and PZT mirror vibration of the interferometer. A theoretical analysis has been performed that explains the observed phenomenon. It has been shown that the wavelength change due to injection current is controlled by the interferometer. The dependence of wavelength change on the injection current variation is calculated using a model of coupled resonators consisting of the laser cavity and the interferometer. The fringe phase change caused by modulation of injection current is derived from it. The calculated phase fluctuation agrees well with those observed in experiments.

A novel low cost, non-contact optical vibration sensor requiring only a single optoelectronic component has been developed. It consists of a CW semiconductor laser operating with external optical feedback. The laser beam reflected from a target generates a series of lasing modes set by the external cavity length. Beating of the modes produces an RF signal and this signal is detected as a variation in the junction voltage. Any change in the external cavity length induces corresponding beat frequency variations in the RF signal, which are transformed into amplitude variations using a simple edge-detection filter system. Using this sensor, low amplitude vibrations have been measured at frequencies of up to 600 Hz. Successful results have been achieved with target reflectivities lower than 5%. When calibrated, the sensor demonstrates satisfactory output for submicron vibration amplitudes. Maximum amplitudes of 1 mm have been measured with an accuracy of 0.2%.

In the proposed design of the spectrometer provision has been made to measure the reflectivity, transmittance and scattering factor of laser mirrors and their glass blanks before actual coating. The spectrometer is in the form of a double beam ratio recording system and works on the principle of modulation radiometry. The design is expected to provide lower value of uncertainty, on the order of 5 part in 10000 in the measurements, because of use of integrating sphere, solid state signal processing electronics and single photodetector. The remarkable features of this design are: ambient light does not affect the measurements and care has been taken to reduce the effects of source fluctuations and polarization due to presence of optical components.

The increasing complexity of semiconductor devices and corresponding dimensions decreasing till the most advanced semiconductor chips manufactured in 0.35 micrometers or 0.25 micrometers need more cleanliness technological conditions. From this wide field the particles are not even detected or detectable in today's fabs will become killer contaminants of future technology of 0.18 micrometers . The particle must first be detected before they can be eradicated. For this reasons the most recommended investigation apparatus are optical particle counters and condensation nucleus counter for determining of airborne p article concentration and as ultrapure water chemicals, gases and vacuum particle counter. In the paper I have analyzed the laser diode application as light sources with the counting results sizing data generation and performance parameters which shown the benefits of their using. All the systems presented can be used for monitoring of particle concentrations for ultrapure fluids from microelectronics fab processes and can be recommended to all microelectronics fabs.

In this paper we present results of our interferometric system for embedded optical fiber in composite material, where a laser diode is used as light source. Optical phase changes induced by laser diode injection current modulation are characterized in order to apply an optoelectronic setup for stabilization and optical phase modulation. He-Ne source versus laser diode are compared for the system. Details on parameter characterization, specially visibility drift and environmental disturbance impact, are analyzed. Experimental design and the results observed are also given.

Short-range laser rangefinders are the object of intense research effort due to their wide range of applications in tasks such as machine vision, automated inspection and 3D range map acquisition. For ranges of up to a few meters, Amplitude Modulation Continuous Wave (AMCW) systems using modulation frequencies in the range of several MHz, have obtained very interesting results. However, these systems presents a trade-off between maximum range and minimum measurement resolution, which is indeed a problem. In this work we present the conception and first experimental results of an AMCW system that employs two different modulation frequencies to overcome this problem and achieve both wide measurement range and good resolution.

Tunable diode lasers have become a light source of choice for spectroscopic applications because of their small size, high efficiency, reliability, and low cost. Tuning for a particular wavelength is commonly realized by using the Littman-Metcalf external cavity configuration with a diffractive grating and rotating mirror. Using this approach, mechanical moving parts and a high degree of precision in the rotation mechanism are required for wavelength selection. Because of this mechanical motion, the tuning process is relatively slow. In some spectroscopic applications sample probing at more than one wavelength is desirable, which currently requires two or more lasers. The development of a single laser source with fast selection over a definable set of wavelengths, also capable of simultaneous emission of a multi-line spectrum, is described. Such a laser can be used to match the spectral signature of the sample and would dramatically increase the speed and reliability of a laser spectrometer. The design is based on an external-cavity configuration with fast computer controlled (in the millisecond range) line selection and has no moving parts. The laser is capable of emitting sets of multi-line near infrared spectra, each spectrum stored as a record in a computer database and matching the spectral signature of a particular chemical component, thus facilitating rapid and reliable spectroscopic detection and analysis of compound samples. The laser design and experimental test results are presented and discussed in the paper.

Laser light can enable electronic displays with unique properties. Direct write laser display systems using point scanning or line scanning have been developed. Emerging, high information content, large screen displays based on small 2D liquid crystal on CMOS light valves and projection optics provide electronic images with unprecedented quality. This paper will describe the advantages that can be provided by laser illumination applied to display systems if significant technical and economic barriers can be overcome.

This paper discusses a high-brightness multi-laser source developed at Polaroid for such applications as coupling light to fibers, pumping fiber lasers, pumping solid state lasers, material processing, and medical procedures. The power and brightness are obtained by imaging the nearfields of up to eight separate multi-mode lasers side by side on a multi-faceted mirror that makes the beams parallel. The lasers are microlensed to equalize the divergences in the two principal meridians. Each laser is aligned in a field- replaceable illuminator module whose output beam, focused at infinity, is bore-sighted in a mechanical cylinder. The illuminators are arranged roughly radially and the nearfields are reimaged on the mirror, which is produced by diamond machining. The array of nearfields is linearly polarized. A customizable afocal relay forms a telecentric image of the juxtaposed nearfields, as required by the application. The lasers can be of differing powers and wavelengths, and they can be independently switched. Light from other sources can be combined. The output can be utilized in free space or it can be coupled into a fiber for transport or a fiber laser for pumping. A linearly polarized free space output can be obtained, which allows two units to be polarization combined to double the power and brightness.

We report on our efforts to develop a laser printbar consisting of a very dense array of independently addressable laterally-oxidized top-emitting VCSELs. In order to maintain wafer planarity for easy electrical routing, the buried oxidation layer in our structure is accessed through small via holes instead of a more typical mesa etch. Unlike most VCSELs, our devices utilize transparent indium-tin- oxide top contacts that allow for a more compact device design. The 200-element array we fabricated has a linear density of one device every 3 micrometers .

A1GaInP visible laser diode is one of the most attractive light sources because it is of great importance in many applications such as optical information storage systems, laser printers, bar code readers and laser pointers. A1GaInP laser diode has a broad emission spectrum of 610 to 690 nm that makes it a versatile and outstanding light source. In addition, AlGaInP laser diodes with low threshold currents have also been realized. The laser diode used for our study is a 660-nm compressively strained A1GaInP with a structure of double-channel ridge waveguide (DCRW). Laser diodes with DCRW structure are widely used for commercialized low-cost and low-power laser diode applications owing to their relatively low threshold currents, easy fabrication and high yield as compared to laser diodes with selectively buried ridge waveguide structure. However, the top surfaces of DCRW laser diodes are non-flat and heat dissipation becomes a main problem for DCRW A1GaInP laser diodes. Especially, if comparing A1GaInP laser diodes with A1GaAs laser diodes, A1GaInP laser diodes have lower thermal conductivity and higher thermal resistance. Therefore, a good die bonding becomes important for improving the heat dissipation of DCRW AlGaInP laser diode chips. Most studies for die bonding have been focused on the choice of submounts or heat sinks with large heat conductivity. Few investigators study how to improve the quality of die bonding and avoid leading voids inside bonded interface. In this study, different p-metal materials, p-metal annealing environments, die-bonding steps and die-bonding equipment were adopted to change die-bonding conditions. Their influences on thermal dissipation capability were also investigated.

High-power single transverse-mode 1.06 micrometers laser diodes are important for replacement of Nd:YAG lasers as fundamental light sources for green SHG lasers. Our Al-free InGaAs SQW laser diodes [InGaAs/InGaAsP/InGa(As)P] grown by low-pressure MOVPE have shown that the increased In composition over 1.06 micrometers deteriorates basic characteristics; that is, increased threshold current and shorter lifetime. The tensile-strained high-bandgap (In)GaAsP barrier layers are incorporated to compensate high compressive strain of an InGaAs quantum well to suppress the overflow of electrons from a quantum well. For 50-micrometers wide broad area lasers, the threshold current is reduced and the lifetime is markedly improved by using strain compensating barrier layers. For single transverse mode operation, the buried ridge structure with a high bandgap AlGaInP current blocking layer is employed in order to avoid the excess current leakage. With using these schemes, almost temperature insensitive light-current curves have been obtained over 20 - 80 degree(s)C. For a device as cleaved, the threshold current increases from 17.1 to 21.7 mA for the temperature range of 20 - 80 degree(s)C. The slope efficiency of 0.4 W/A/facet is unchanged for the same temperature range up to 60 mW/facet. Characteristic temperature T0 for the threshold current is 437 and 175 K for the temperature range of 20 - 50 and 50 - 80 degree(s)C, respectively.

Narrow linewidth (< 100 KHz) semiconductor lasers are expected to be a key technology in NASA's stellar interferometry missions to search for planets around nearby stars. Long coherence length lasers are needed for precise (20 pm to 5 nm) measurements of the optical path difference. This work discusses results using the self-heterodyne delay technique to measure 1.3 um InP based DFB lasers. We will also address practical issues concerning detection and elimination of back reflections, choice of fiber length and resolution, and measurement of laser l/f and current supply noise.

In very demanding optoelectronic sensor applications it is necessary to encapsulate semiconductor components hermetically in metal housings to ensure reliable operation of the sensor. In this paper we report on the development work to package a laser diode transmitter module for a time- off-light distance sensor application. The module consists of a lens, laser diode, electronic circuit and optomechanics. Specifications include high acceleration, -40....+75 degree(s)C temperature range, very low gas leakage and mass-production capability. We have applied solder glasses for sealing optical lenses and electrical leads hermetically into a metal case. The lens-metal case sealing has been made by using a special soldering glass preform preserving the optical quality of the lens. The metal housings are finally sealed in an inert atmosphere by welding. The assembly concept to retain excellent optical power and tight optical axis alignment specifications is described. The reliability of the laser modules manufactured has been extensively tested using different aging and environmental test procedures. Sealed packages achieve MIL- 883 standard requirements for gas leakage.

Expanded mode alignment tolerant optical structures will play an important role in low-cost, large-scale packaging of optoelectronic devices. In this paper, we present two expanded mode structures for operation at 1.55 micrometers . Our devices use single epitaxial growth and conventional fabrication schemes. High butt-coupling efficiencies (> 40%) to a single mode fiber with relaxed alignment tolerances were achieved. The first of our devices uses adiabatic transformation over 500 micrometers . The second device uses resonant coupling over a much shorter region of 200 micrometers . The second scheme offers an interesting possibility for monolithic integration of active-passive components. We present the design and simulation results of such an integrated device.

High-power diode lasers such as `cm-bar arrays' are important for many applications. The `p-side down packaging', i.e. the direct mounting of the epitaxial layer sequence on a heat spreader ensures sufficient thermal properties, however, in such a geometry, additional mechanical strain of the active region represents a central issue, affecting both the laser parameter as well as lifetime and reliability of the device. Thermally induced strain caused by device packaging is studied in high-power semiconductor laser arrays by a novel non-invasive technique. Photocurrent measurements with intentionally strained laser array devices for 808 nm emission reveal spectral shifts of all allowed optical transitions in the active region. These shifts serve as a measure for strain and are compared with model calculations. Depending on the specific heat spreader materials we find compressive or tensile mounting induced strain contributions. For a given packaging architecture, about one quarter of the mounting induced strain is transferred to the quantum well region of the device. Spatially resolved measurements allow to measure lateral strain gradients in the devices. Using this data for calibration we show that polarization resolved electroluminescence scans can be used as convenient measure for strain homogeneity test also in quantum-well devices.

An optical module is assembled using a passive-alignment technique. A laser diode (LD), a single mode fiber with a ferrule and a monitor photo diode (PD) are mounted on a silicon (Si) substrate. The LD and the PD are adjusted in three axis direction (horizontal axis, light axis and horizontal angle axis) to be die-bonded. The fiber is laid between a V-groove on the Si substrate and a glass block. In the perpendicular axis direction, the V-groove width is set so that the LD active layer and the fiber core are at the same height. The optical devices and the fiber facet are sealed using a thermosetting resin material. The Si substrate is bonded in a nonhermetic-sealed plastic package. The coupling losses of the LDs to the butt-jointed single mode fibers are estimated to be 7.4 to 10.8 dB, to the average value of 8.6 dB. The tracing errors of the fabricated modules are less than +/- 1.5 dB at ambient temperature from -40 to +85 degrees centigrade. The coupling losses change at the damp-heat stress test (85 degrees and 85% RH) is less than +/- 0.5 dB after more than 5,000 hours.

We have performed four wave mixing (FWM) measurements on a 2-section semiconductor optical amplifier (SOA) using CW and pulsed pump and probe beams. The FWM efficiency depends on the input pump power, the gain of the 2-section SOA and the wavelength separation between the pump and probe beams. A -19.1 dBm FWM signal power from the amplifier is achieved when the wavelength difference between the pump and probe beams is 2.5 nm. The pulse amplitude and pulse width of the FWM signal under the condition when the FWM signal is generated using pulsed pump and probe beams has been measured and analyzed. The results of the analysis are in agreement with the experimental data.

Semiconductor laser diode arrays are becoming a widespread source for a large variety of applications, ranging from telecommunications to industry. In particular, the availability of low-cost high-power laser diode arrays makes it possible their use in industrial context for material cutting, welding, diagnostics and processing. In the above applications the exact control of the beam quality plays a very important role because it directly affects the reliability of the final result. We have developed a characterization technique which, starting from total intensity measurements on planes orthogonal to the beam propagation path, is able to deduce the working conditions of each laser setting up the array. The importance of this approach is twofold. First it allows a non destructive quality control on ready-to-use laser arrays; second it may represent a powerful tool for the detection of design problems in the array itself and in the bias circuitry as well. The problem is formulated as an inverse one and the solution is found by minimizing a proper functional. Several numerical experiments have been performed and the results clearly indicate the ability of the proposed approach tin identifying specific failures in a laser diode array, such as single element power drop.

Packaging is one of the most critical operation in optoelectronics manufacturing. Optoelectronic packages for semiconductor laser diodes must provide submicron alignment between optical elements, high-speed electrical connections, excellent heat dissipation, and high reliability. We propose the use of composite substrate materials that simplify the design of optoelectronic packages, improve thermal and mechanical performance, and are suitable for high- reliability applications.

Grating coupled surface emitting lasers (GCSELs) are in- plane lasers monolithically integrated with grating outcouplers for beam shaping and image generation. Highly directional and efficient outcouplers can be formed using various grating and waveguide geometries. Beam shaping features are incorporated using a computer generated waveguide hologram that allows the wavefront of the emitted light to be tailored for the required beam shape. Requirements on the integrated in-plane laser include a wide and spatially coherent guided wave with a minimum of wavefront distortion and a stable emission wavelength. Promising lasers for this purpose are master-oscillator power-amplifier configurations as well as various kinds of unstable resonator designs. Here we present results from modeling and experiments on the key elements of GCSELs as well as fully integrated GCSELs of linear and circular geometries.

In this paper results from the evaluation and comparison of the analog performance of laser transmitters from several different manufacturers will be reported. The bulk of the tested devices were commercially available InGaAsP edge- emitters (1- and 4-way packages). The evaluation of the lasers is based on a semiautomatic setup that characterizes static properties such as slope efficiency, noise and linearity. The measured data is visualized in a compact way with system pass/fail criteria that enables easy comparison and selection of different laser diodes with respect to system noise, deviation from linearity an operating range.

We have studied the spatial and spectral characteristics of vertical-cavity surface-emitting laser emission using near- field scanning optical microscopy. We report the multi- transverse-mode characteristics of 15 micrometers diameter proton- implanted 850 nm devices used in a 2 Gbit/s multimode fiber- optic links. Spectrally resolved and integrated intensity scans over a 20 X 20 area were performed. The intensity of each resolvable transverse mode was integrated and its wavelength range false-colored at each scan position. The resulting composite image displays relative intensity and spatial distribution information for each transverse mode. Correlation with the shear force data allows mapping of the optical distributions to topographical features. Lasing filaments were observed at high drive currents. Gain competition among spatially overlapping transverse modes was observed while spatially isolated modes coexisted without competition.

The degradation of GaAlAs/GaAs laser diode bars mounted on copper micro channel heat sinks was investigated using optical microscopy, scanning electron microscopy and EDX- spectroscopy. The high power diode lasers were characterized before and after burn-in and after long term lifetests. Changes in surface morphology and surface composition of the facets were detected as well as changes in threshold current, slope efficiency and wavelength. Due to the degradation threshold current increases and slope efficiency decreases while the wavelengths were shifted to higher values showing a broader spectral width. The influence of these changes on performance and lifetime of the high power diode lasers will be discussed.

We disclose a method of eliminating the polarization instability in laterally-oxidized vertical-cavity surface- emitting lasers. By employing an appropriately-shaped device aperture, we are able to make the lasers operate in a single polarization direction through their entire L-I curve.

In order to overcome catastrophic optical damage, decoupled confinement heterostructure (DCH) featuring a broadened waveguide and thin carrier block layers have been developed. Due to decoupling of carrier and optical confinement, a DCH laser can be designed more flexibly than a conventional separated confinement heterostructure laser, i.e., laser diodes can be designed with a variety of gain coupling factor (Gamma) (perpendicular), quantum-well number NW, keeping the beam divergence angle constant.

High power near diffraction limited external cavity semiconductor tapered lasers that use a single-angled-facet input preamplifier are demonstrated for the first time. Four electrodes (three in the preamplifier region and one in the power section) on the device were implemented to investigate the switching contrast ratio of the output laser intensity. More than 1 W CW of power was obtained with a slope efficiency of 0.7 W/A, and close to 20 dB intensity contrast ratio was obtained by switching off two and three electrodes in the input ridge section. Also, more than 50 dB side-mode suppression ratio and 60 nm tuning bandwidth were obtained. These powers were found to be emitted in a near-diffraction- limited beam.

Diffractive optical elements (DOE) have been widely used in both scientific and industrial applications. Optical wavefront measurements are one of the most important methodologies in verifying the performance of DOEs. Due to its non-destructive nature, ease of implementation, and relative short operation time, optical interferometry-based systems for wavefront measurements remain popular. The advantages and drawbacks of a non-common path and common path interferometry technique are examined first within this article.

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Journal of Applied Remote SensingJournal of Astronomical Telescopes Instruments and SystemsJournal of Biomedical OpticsJournal of Electronic ImagingJournal of Medical ImagingJournal of Micro/Nanolithography, MEMS, and MOEMSJournal of NanophotonicsJournal of Photonics for EnergyNeurophotonicsOptical EngineeringSPIE Reviews